STUDY ON THE CEMENTITIOUS MORTAR FOR SEMI-FLEXIBLE PAVEMENT

Transcription

1 STUDY ON THE CEMENTITIOUS MORTAR FOR SEMI-FLEXIBLE PAVEMENT Shuguang Hu, Shaolong Huang, Qingjun Ding and Rongkun Zhang Key Laboratory for Silicate Materials Science and Engineering of Ministry of Education, Wuhan University of Technology, China Abstract Semi-flexible pavement is a kind of composite pavement that utilizes the pore structure of open-graded asphalt mix which is subsequently filled with an appropriate cementitious mortar. The main purpose of this research was focused on the influences of W/B ratio, S/B ratio and using of superplasticizer on the performance of cementitious mortars for semiflexible pavement. 14 kinds of mortars were designed and studied to investigate the trends of the mortars with different W/B ratio, S/B ratio and superplasticizer dosage. Based on the study, cementitious mortar with the combinations of good workability, high strength and low drying shrinkage was prepared by using polycarboxylic acid superplasticizer and expansion agent under the proper mix proportions. The evaluation of the semi-flexible pavement material containing this kind of cementitious mortar indicated its high capacity and great potential to reduce the permanent deformation under high temperature and heavy traffic loading. 1. INTRODUCTION By the end of 2007, the expressway of China had exceeded 50,000km. Most of them were newly constructed with flexible pavement material after the year However, due to the increasing of traffic volume and traffic load, rutting occurred in a large amount of expressways during the first and second summer after the expressways were open to traffic. A kind of new way was developed to solve rutting problem and increase the loading capacity of asphalt pavement by using semi-flexible pavement material. Traditionally, road pavements are generally categorized into two broad classification or type, namely the flexible pavement, such as asphalt pavement and the rigid pavement, such as Portland cement concrete pavement. Both types of pavements have their advantages and disadvantages. For example, concrete pavement is cost effective and durable, but difficult to repair and less comfortable during driving compared with asphalt pavement. Semi-flexible pavement is a kind of pavement combining the best properties of asphalt and concrete. It is applied as open-graded asphalt in which the voids are filled with cementitious mortar. In this way, the semi-flexible 1237

2 pavement combines the flexibility and freedom of jointless asphalt concrete and the excellent bearing capacity and wear resistance of cement concrete. Studies done by Setyawan [1] and Mayer [2] showed that semi-flexible pavement had high capacity, long durability, chemical and freeze/throw resistance. Throughout Europe and the United States, an increasing interest in this type of pavement has been developed in recent years. [3-5] In Denmark, the United States, Germany and Netherlands, semi-flexible pavements have been laid in several airports, highway, ports and bus terminals. It was found in the research and application that the key issue of semi-flexible pavement material is the performance of the cementitious mortar. [6] The former studies usually focused on the strength and flowability of cementitious mortar. Superplasticizer and ultra-fine powders such as crushed quartz and silica fume were used to prepare cementitious mortar with high strength and flowability. [5-7] However, a disadvantage of such pavement material can be the appearance, which could be mainly caused by the shrinkage of the cementitious mortar. [6,8] Hence, the cementitious mortar should have proper strength, which offers the capacity for the material, excellent workability, which makes sure the mortar can be fully filled with the connected void of open-graded asphalt mix, and low shrinkage, which prevent the pavement from cracking. In this study, the focus was given on the influences of the superplasticizer type, sand/binder ratio and the addition of expansion agent on not only the workability and strength of the cementitious mortar, but also its volume stability. Several kinds of cementitious mortar with different formulas were designed and analyzed to optimize the mix proportion. Then semi-flexible material was prepared by filling the selected mortar to the open-graded asphalt specimen and the performance of the semi-flexible pavement was evaluated compared with normal asphalt concrete. 2. EXPERIMENTAL DETAIL 2.1 Materials The cement used in the test was OPC 42.5 from Huaxin Cement Co., Ltd, Hubei, China. Sand used in the test consisted of clean, sound, durable, particles of processed silica sand that meet the requirements for wear and soundness specified for coarse aggregate. The sand should contain no clay, silt, or other objectionable matter. Table 1 represents the gradation limitation of the sand used in the test. Table 1 Sand for cementitious mortar Sieve size/mm Percent passing by weight/% Two kinds of superplastisizer, naphthalene type (FDN-9001) and polycarboxylic acid type (Melflux 2651F) were used and compared in this study. The naphthalene type superplasticizer was produced by Wuhan Haoyuan Chemical Co. Ltd. The polycarboxylic acid type superplasticizer was produced by BASF Chemical. Both types of superplasticizer were powder. Expansion agent was UEA obtained from Wuhan Sanyuan Chemical Co. Ltd. 1238

3 2.2 Methods and procedure Workability of the mortar In the former studies, the workability of the cementitious mortar for semi-flexible pavement was only tested and evaluated by funnel flow test as usual, through the dimension of the funnel and the required flow time are different. For example, 12~13 seconds is required during 1L funnel test in most of European countries, [5] 8~10 seconds is required in the United States in the same test.[4] However, according to the research and application in China, the cementitious mortar would not work as it was supposed when the flowability is reasonable in the funnel flow test. The main problem is the high bleeding rate when the flowability of mortar is too big. Therefore, the workability of the mortar was evaluated by both its flowability and bleeding rate in this study. The flowability was tested through funnel test. The volume of the funnel used in the test was 1.725L. The bleeding rate was performed as the specification of Masonry Cement (GB/T ). [9] Further more, the flow time of the mortar after 0.5h was tested to estimate the flowability losing of the mortar Mechanical performance of the mortar The compressive strength and tensile strength of the mortar were tested after 7days and 28 days curing according to Method of testing cements Determination of the strength (GB/T ). [10] Volume stability of the mortar The volume stability of the mortar was estimated by drying shrinkage. The test was conducted under the specification of Test Methods for the Fundamental Performance of Masonry Cement (JTJ 70-90). [11] The drying shrinkage value was measured at 1d, 3d, 7d, 14d, 28d, 45d and 60d Preparation of the semi-flexible material The open-graded asphalt mixture with void content of 30% and connected void content of 26% was used in the study. It was composed of basalt, limestone filler and SBS modified asphalt. The asphalt content of the mixture was 3.2%. The mix gradation is shown in table 2. Table 2 Mix gradation of open-graded asphalt mixture Seive size/mm Passing /% Three kinds of open-graded asphalt specimens were mixed and compacted to prepare semi-flexible pavement material. They were cylindrical sample with 150 mm in height and 100 mm in diameter for compressive strength and compressive modulus, cylindrical sample with 63.5 mm in height and mm in diameter for indirect tensile strength, and slab with the dimension of 300mm 300mm 5mm for the wheel tracking test. The bottom and the side were sealed when the mortar was filling to the specimens. The mortar penetrated and filled the void all by its flowability. No vibration should be taken during the whole test. When the filling was finish, the mortar on the surface of specimens was scraped to make the texture of the open-graded asphalt mixture revealed. The weight of specimens before test and after the hardening of mortar was measured to calculate the volume properties of the semi-flexible pavement specimens. 1239

4 2.2.5 Evaluation of the semi-flexible material Compressive strength and modulus, indirect tensile strength and wheel tracking test were conducted to evaluate the performance of the semi-flexible pavement material. Measurement of compressive strength, compressive modulus and indirect tensile strength were performed on Instron 1314 according to Uniaxial Compression Test for Asphalt Mixtures (T ) [12] and Indirect Tensile Test for Asphalt Mixtures (T ). [12] Both of the tests were under 20. Wheel tracking test was taken to evaluate the rutting resistance property of the asphalt mixture according to Wheel Tracking Test for Asphalt Mixtures (T ).[12] 2.3 Mix design In order to study the influences of the superplasticizer type, sand/binder ratio and the addition of expansion agent on the workability, strength and volume stability of the cementitious mortar, 14 kinds of cementitious mortars with different formulas were designed. The formulas of the mortars are shown in table 3. Table 3 Mix proportion of cementitious mortars No. Superplasticizer Binders Pencentage of binders W/B S/B Water Sand polycarboxylic ratio ratio Cement UEA naphthalene acid / / / / / / / / / / / / / / / EVELUATION AND DISCUSSION OF THE CEMENTITIOUS MORTAR Testing results of all kinds of mortars are shown in table 4 and evaluated and discussed as follow. 3.1 Workability Flow time The curves of influences of W/B ratio, S/B ratio, the type and dosage of superplasticizer on the flow time of cementitious mortar are shown in Fig

5 Table 4 Test results of cementitious mortars No. Compressive Tensile Drying shrinkage Flow time/s Bleeding strength/mpa strength/mpa after 60d rate/% Fresh 0.5h 7d 28d 7d 28d /microstrain (a) (b) (c) Figure1: The curve of flow time test. (a) the influence of W/B ration; (b) the influence of S/B ration; (c) the influence of superplastisizer type and dosage. 1241

6 As the observation of preparation test of semi-flexible pavement specimens, a minimal flowability of 15s was necessary. From the results obtained, the flow time of the fresh mortar mixtures was between 10s to 18s, most of them was between 11s and 14s. With the increase of W/B ratio, superplasticizer dosage and decrease of S/B ratio, the flowability of the mortar was increased. However, when the S/B ratio was too low or the dosage of superplasticizer was too high, the losing of flowability increases. As far as the type of superplasticizer was concerned, the water reducing rate of polycarboxylic acid type was obviously higher than that of naphthalene type. The dosage of the polycarboxylic acid type was nearly half of naphthalene type when the same flowability was achieved. Moreover, the addition of polycarboxylic acid superplastisizer provides excellent plasticizing effect, which made the flowability losing of mortars containing polycarboxylic acid superplastisizer was much lower than mortars prepared with naphthalene type Bleeding rate Only high flowability is not enough for the mortar used to prepare semi-flexible pavement. Because the big W/B ratio and high dosage of superlasticizer may lead to the bleeding and segregation of the mortar, which would plug up the pore when the mortar is poured in opengraded asphalt mix. (a) (b) (c) Figure2: The curve of bleeding rate test. (a) the influence of W/B ration; (b) the influence of S/B ration; (c) the influence of superplastisizer type and dosage. 1242

7 Fig. 2 shows the curves of the bleeding rate tests of mortars. It can be indicated that the increasing of W/B ratio leads to a high bleeding rate of mortars, especially under high value as 0.5% and 0.55%. The same situation occurred when the dosage the naphthalene superpasticizer increased. However, when polycarboxylic acid superplastisizer was used, the excellent plasticizing effect made the mortar uniform and harmonious. For S/B ratio, despite of the improvement of the flowability, the reducing of S/B ratio also led to a higher bleeding rate due to the absolute weight of the water in the proportion was enhanced. However, this status would be unobvious when the S/B ratio was higher than Mechanical performance As the results in table 4, also the fundamental of cement-based material, the mechanical property of the mortars was mainly affected by W/B ratio. It is shown in Fig. 3a that the compressive strength dropped to only 23.3 MPa after 28d at W/B ratio At the same W/B ratio, the increase of superplasticizer made the compressive strength of the mortar decrease slightly. Furthermore, it is indicated from Fig. 3b, the changing of S/B ratio also affected the compressive strength of the mortar. When the S/B ratio was at lower value, the compressive strength was increased with the increasing of S/B ratio because of the defect caused by the increase of absolute water weight of the proportion. However, when S/B ratio was higher than 0.25, the compressive strength decreased due to the reducing of cement binders in the proportion. (a) (b) Figure 3: Influence of mix proportion on the compressive strength of mortars. (a) W/B ration; (b) S/B ratio 3.3 Volume stability Drying shrinkage of the mortars, as shown in Fig. 4(a) and Fig. 4(b), was influenced by W/B ratio and S/B ratio of the mix proportion. Higher W/B ratio and lower S/B ratio led to high value of drying shrinkage. From the results obtained, when W/B ratio changed from 0.4 to 0.55, the shrinkage value enlarged from 3000microstrain to nearly 5000microstrain after 60 days. The shrinkage value of mortar with no sand (proportion No.10) was even the same as mortar with the highest W/B ratio (proportion No.4) despite its lower W/B ratio. This situation may caused by the increasing of cement binders and the absolute water dosage. As far as the influence of expansion agent was concerned, as shown in Fig. 4(c), the shrinkage value of the mortar without UEA was extremely larger compared with mortars containing UEA. Besides the lower shrinkage value, the shrinkage of mortars containing UEA 1243

8 mainly concentrated in the early stage after the hardening of the mortars. After 14 days, the rate of shrinkage descended rapidly. However, the shrinkage of the mortar without UEA in its proportion was obvious after 30 days. This situation is essential for the mortars prepared for semi-flexible pavement. Because there is often 7 days curing time before the pavement is open to traffic. In this period, measures, such as splashing water and covering, can be conducted to restrict dry shrinkage. But nothing could be done if the pavement is open to traffic. (a) (b) (c) Figure 4: Influence of mix proportion on the drying shrinkage of mortars. (a) W/B ratio; (b) S/B ratio; (c) addition of expansion agent 1244

9 4. PERFORMANCE OF THE SEMI-FLEXIBLE PAVEMENT Based on the discussion above, proportion No.8 was selected to prepare semi-flexible pavement due to its combination of good workability, high strength and low drying shrinkage. The results of semi-flexible pavement material after 28 days curing are shown in table 5. The performance data of asphalt concrete and cement concrete is achieved from the Specification of Cement Concrete Pavement Design for Highway (JTG D ) and Specification for Design of Highway Asphalt Pavement (JTG D ). The asphalt concrete was AC-20 with polymer modified asphalt binders. And type of the cement concrete was C30, the normal strength for concrete pavement in China. Table 5 Performance test results of semi-flexible pavement material Air void/% Compressive strength/mpa Compressive modulus/mpa Indirect tensile strength/mpa Dynamic Stability /cycles/mm Semi-flexible Asphalt concrete Cement concrete / / 1) Volume property. The air void of semi-flexible pavement material was 4.7%. Considering the 4% of unconnected void in the total 30% void of the open-graded asphalt mix, over 97% of connected void (26%) was filled with cementitious mortars. 2) Mechanical performance. It can be seen from table 5 the mechanical test value of semiflexible pavement material was between that of asphalt concrete and cement concrete, which indicated that the semi-flexible pavement material was neither too flexible nor too rigid. Furthermore, compared with cement concrete, the mechanical performance of semi-flexible material is close to asphalt concrete, which accords with the concept of semi-flexible. 3) Wheel tracking test. As it is shown in table 5, the DS of semi-flexible pavement material reached 36000cycles/mm, over 10 times of asphalt concrete with polymer modified asphalt binders. It can be concluded from the comparison that semi-flexible pavement had a great potential to reduce the permanent deformation under high temperature and heavy traffic loading. 5. CONCLUSIONS W/B ratio, S/B ratio and superplasticizer dosage have big influences on the workability, mechanical strength and volume stability of cementitious mortar for semi-flexible pavement. The mortar with combination of good workability, high strength and low drying shrinkage can be prepared by selecting appropriate mix proportion. Compared with naphthalene type, polycarboxylic acid superplasticizer is fit for mortar semi-flexible pavement due to its high water reducing rate and excellent plasticizing effect. The addition of expansion agent can obviously decrease the dry shrinkage value of the mortars, especially after 14 days. The evaluation of the semi-flexible pavement material indicated its high capacity and great potential to reduce the permanent deformation under high temperature and heavy traffic loading. 1245

10 ACKNOWLEDGEMENTS The authors would like to appreciate the financial support of Hi-tech Research and Development Program of China (863), Ministry of Science and Technology, China (Project number: 2006AA11Z117). REFERENCES [1] Setyawan, A., Development of Semi-Flexible Heavy-Duty Pavements. PhD thesis. University of Leeds. Leeds [2] Mayer, J. and Thau, M. Joint less pavements for heavy-duty airport application: the semi-flexible approach. Proceedings of the 27th International Air Transportation Conference. Chicago, Illinois, USA, 2001, pp [3] EAPA. Airfield use of asphalt. May 2003, [4] Robert J. et al. Selecting a Rut Resistant Hot Mix Asphalt For Boston-Logan International Airport. roystonlab.com. [5] Densit a/s. Densiphalt Handbook. Aalborg, [6] Hassan K.E., Setyawan, A. Zoorob, S.E. Effect of Cementitious Grouts on the Properties of Semi- Flexible Bituminous Pavements. Proceedings of 4th European Symposium on Performance of Bituminous and Hydraulic Materials in Pavements. Nottingham, UK, 2002, pp [7] Koting S., Mahmud H. and Karim M. R. Influence of superplasticizer type and dosage on mortar for semi-flexible pavement application Journal of the East Asia Society for Transportation Studies, Vol. 7, 2007, pp [8] C. P. Plug, A.H. de Bandt, B.J. van der Woerd and G. Steensma. Improved performance grout macadams high performance application of grouted macadam. [9] GB/T , Masonry Cement. State Bureau of Quality and Technical Supervision, China (in Chinese) [10] GB/T , Method of testing cements Determination of the strength. State Bureau of Quality and Technical Supervision, China (in Chinese) [11] JTJ Test Methods for the Fundamental Performance of Masonry Cement. Ministry of Construction, China (in Chinese) [12] JTJ , Standard test methods bitumen and bituminous mixtures for highway engineering. Ministry of Communication, China (in Chinese) 1246